Does anyone know why a halo orbit was chosen for the relay sat instead of a regular, lunar orbit?† I know that due to the moon's lumpy gravitational field, there are only a few stable orbits available, but anything orbiting a Lagrangian point is going to require stationkeeping adjustments regardless, right?

†I understand that that would put the lander out of contact during that part of the relay-sat orbit, but it would also completely rule out a major source of potential radio interference during observational periods, which strikes me as an even more important consideration. Data can be stored and batched, after all.